Protective arrangement for electric power lines



Feb. 13, 1934. R Q P ET AL 1,946,859

PROTECTIVE ARRANGEMENT FOR ELECTRIC .POWER LINES Original Filed May 23,1929 4 Sheets-Sheet l fwvewfar:

Feb. 13, 1934. R. o. KAPP Er AL 1,946,859

PROTECTIVE ARRANGEMENT FOR ELECTRIC POWER LINES Original Filed May 25,1929 4 Sheets-Sheet 2 B DRI DR? 6 (BI 01.! 1 CB2 [71 venfora: E.01112;); 05 C, 6. CCZIkOZfAe/Q" Feb. 13, 1934. R. o. KAPP ET AL1,946,359

PROTECTIVE ARRANGEMENT FOR ELECTRIC POWER LINES Original Filed May 25,1929 4 SheetsSheet 3 AA uif Ail array Feb. 13, 1934. R o KAPP r AL1,946,859

PROTECTIVE ARRANGEMENT FOR ELECTRIC POWER LINES Original Filed May 23,1929 4 Sheets-Sheet 4 OLA nnmm

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Patented Feb. 13, 1934 UNITED STATES PATENT OFFICE PROTECTIVEARRANGEMENT FOR ELECTRIC POWER LINES Reginald Otto Kapp and CharlesGeorge Carrothers, London, England Serial No. 641,940

8 Claims;

system of which the line or cable forms a part, the

general object of such arrangements being to isolate only the faultysection, while the remainder of the system remains in service.

The principal object of the invention is to provide such arrangementswhich will permit of the pilot wire being located in such a positionrelative to the conductors carrying the power that the occurrence of afault might cause the pilot wire, as well as the power conductors, to bebroken.

One of the features of the present invention is a protective arrangementin which a pilot wire embedded in the cable containing the powerconductors is utilized, the controlling arrangements being such thateven if the pilot wire is broken he automatic isolation of the sectionis permitted when a fault occurs.

Another feature of the present invention is a protective arrangement inwhich a pilot wire forms one of the strands of a stranded earthing wirein an overhead transmission line located on the same standards as thepower conductors, the controlling arrangement in this case also beingsuch that even if the pilot wire circuit is broken the completeisolation of the section is permitted when a fault occurs. I

These and other features of the invention will be better understood byreferring to the following description with reference to theaccompanying drawings which show by way of example various embodimentsof the invention.

Fig. 1 shows a transmission system including both an overheadtransmission line and an underground cable, together with protectingarrangements suitable for isolating faults according to the individualconditions of the various lines.

Fig. 2 shows a section of stranded earth wire with interlocked strandshaving an insulated pilot wire forming one of the strands for use withoverhead transmission lines.

Fig. 3 shows a section of a cable having a pilot wire embedded thereinfor use with underground transmission lines.

Fig. 4 shows circuit controlling arrangements employed in conjunctionwith a pilot wire and applicable only to sections in which power issupplied from one end.

Fig. 5 shows in greater detail the circuit arrangement shown in thepreceding figure.

Fig. 6 shows circuit controlling arrangements" controlled in conjunctionwith a pilot wire and m resembling circuit arrangements employed in so:quadruplex signalling in which one channel is employed for protectingthe section from faults of the kind in which earth currents aresufficiently great as to change the direction of current flow I orsubstantially arrest the flow of current at one 66 end, i; e; when thedifference between the current flowing into or in the section at one endand out at the other are very considerable, while the other channel isemployed for protecting the section from faults of the kind in which theleakage is 70 comparatively small as in underground cables and isdetermined by the different manners in which current or power measuringdevices at each end of the section respond to the current V powerflowing at the end with which they are associated.

Referring to Fig. 1, this shows a complete transmission of three phasehigh tension alternating current comprising the underground cable 1 andthe overhead transmission line 2. The staso tions A and B are generatingstations adapted to supply power to the system or take power from thesystem according as to whether the local demand for power is below orabove the amount generated locally while station C is purely a powerconsuming station.

While Fig. 1 only shows the protective apparatus in a very schematicmanner, details of the apparatus and its manner of operation will bedescribed more particularly with reference to Figs. 4, 5 and 6 of theaccompanying drawings.

In the case when current is fed to a terminal station where there is nogenerating apparatus, such asthe station C, it will be appreciated thatif a fault occurs, current can only be fed to the fault from station E.Protective arrangements at the upper right hand side of station B andstation C are shown in detail in the left hand sides of Figs. 4 and 5and the right hand sides of Figs. 4 and 5 respectively. Undergroundcables are normally subject to two kinds of faults as distinct from thekind to which overhead transmission lines are subject, namely, faults ofa serious character involving heavy cur rent to earth and faults in thenature of leaks often termed incipient faults. The cable 1 runningbetween the stations A and B is protected from-both these kinds offaults by protective ar ran'gements in these stations, such as are'shownmore in detail in Fig. 6. I10

Referring now to Fig. 4, this shows an arrangement for cutting out afaulty section in the event of current flowing in at one end of asection and either current less than a predetermined value flowing outat the other end, or current flowing in at the other end. This issatisfactory in the case of all faults which cause the voltage to dropnearly to zero. In Fig. 4, l, 2 and 3 represent the section of a threephase transmission line between the stations B and C; CB1 and CB2represent the circuit breakers at opposite ends of the section; 0L1 and0L2 represent overcurrent relays, that is to say relays which operatewhen the current flowing through them exceeds a certain predeterminedamount. These relays are of known type and are arranged so that anexcess of current flowing past the relays in any one or more of thelines 1, 2 or 3 will cause the contacts 5 and '7 to open and 6 and 8 toclose. DB1 and DR2 represent directional relays and are arranged toclose contacts 9 and 11 both when no power is flowing and when power isflowing past the relays into the section and to close contacts 10 and 12when power above a predetermined magnitude less than the predeterminedamount necessary to operate the over-current relays is flowing past therespective relays in the other directions; 13 represents the pilot wire;TCl and TC2 represent the tripping coils of the circuit-breakers CB1 andCB2 respectively; D1 and D2 represent the differential relays arrangedfor duplex working in a manner to be described hereinafter; 14 and 15represent contacts in the pilot wire circuit controlled by the trippingcoils TCl and TC2 respectively. The figure shows the condition with nocurrent flowing at all in the leads 1, 2 or 3. In this condition nocircuits are closed.

The following table indicates the position taken up by the relays 0L1,DB1, D1, 0L2, DRZ, D2 under various conditions on the line:-

Positions of relays Conditions on line 0L1 DB1 D1 0L2 DB2 D2 1. Straightthrough overload current from left to right Down.- D0wn.i Up Down. UpDown. 2. Straight throu hovel-load current from right toleit Down UpDown Down-.. Down. Up. 3. Fault on line ed from both ends with voltageeither up or Down. Down. Down Down..- Down..- Down.

down to near] zero. 4. Fault onlinel from left end only Down Down Up UpDown Down. 5. Fault on line fed from right and only Up Down. DownDown... Down. Up.

In the first case, i. e. straight through current contacts 14 and 15will be opened but this is flowing from left to right, it will be notedthat without effect in this particular case.

a circuit may be traced as follows: earth, battery contacts 9, 6 tomidpoint of winding of relay D1. Here the current divides, one halfproceeding via the upper winding of relay D1, resistance 16 to earth,the other half proceeding via the lower winding of relay D1, contact 14,pilot wire 13, contact 15, lower winding of differential relay D2,contact 12 to earth. Relay D2 is energized and contact 19 is closed.This however is without effect as contact 11 of relay D82 is open.

Under the second condition with straight through current flowing throughfrom right to left it will be noted that the condition is substantiallythe same as in the preceding case, the only difference being in theposition of relays DB1, D1, DB2 and D2.

Referring to the third case in which a fault on the line is fed fromboth ends whatever the volts may be, i. e. either up or right down thenboth the relays DB1 and DR2 will be down. Similarly 0L1 and 0L2 willhave their armatures down. Consequently contacts 9 and 6 will be closedat one end and 11 and 8 at the other. The midpoint of the differentialrelay in each case will therefore be connected to the same potential asfollows: earth, battery, contact 9, contact 6 to the midpoint of relayD1. Earth, battery, contact 11, contact 8 to the midpoint of relay D2.Consequently there would be no current on the pilot wire. Current will,however, flow through the upper windings of relays D1 and D2 through theresistances 16 and 17 respectively to earth. Consequently both theserelays will be energized and contacts 18 and 19 closed. Circuits willtherefore be completed for the tripping coils T01 and TC2 as will bereadily appreciated and the circuit-breaker CB1 and CB2 will thereforebe brought out. In this way the section is isolated. At the same timethe Conditions 4 and 5 are reciprocal and it is only necessary toconsider one and for this purpose it will be taken into considerationwhere the fault on the line is fed from the left-hand end only. Underthese conditions 0L1 will be down, DRl will be down, 0L2 will be up andDB2 will be down. The circuit over the pilot wire can therefore betraced as follows: earth, battery, contact 9, contact 6, lower windingof relay D1. contact 14, pilot Wire 13, contact 15, lower wind ing ofrelay D2, contact '7 to earth. Relay D1 will also receive a currentthrough its upper winding and resistance 16 to earth in a branch of theabove circuit. Consequently relay D1 will not be energized while relayD2 will be energized. The closure of contact 19 completes a circuit forthe tripping coil TC2 as follows: earth, battery, contact 11, contact19, winding of trip ping coil TC2 to earth. The tripping coil energizesand trips the circuit breaker CB2 at the same time opening contact 15.The opening of contact 15 breaks the circuit through the pilot wire andtherefore relay D]. becomes excited through its upper winding only andtherefore energizes and closes contact 18. Tripping coil TCl thereforeenergizes as follows: battery, contact 9, contact 18, tripping coil TClto earth. Tripping coil TCl energizes and cuts out the circuit-breakerCB1 and also opens contact 14. In this way the section is isolated.clear that all that is necessary to cause the circult-breaker CB1 totrip is to change the current in the pilot wire sufficiently whether upor down or, by reversal, to cause the balance in the windings of thedifferential relay D1 to be upset and cause relay D1 to energize.

In practice it may happen that there are considerable fluctuations inpower and, where power may be fed from either end of the line, actualreversals in direction. In order to ensure that no It will be 1 each ofthe lines L1, L2, 3

faulty operation will take place it becomes desirable therefore toensure that the directional relays DB1 and DB2 are more sensitive thanthe over-current relays GL1 and L2. This may be done by providing asufficient margin of current so that GL1 will not operate in case of areversal of direction until the current has reached a larger value thanis necessary to operate relay DRl. The same remarks of course apply torelays 0L2 and DB2. If desired some form of time lag could be providedso as to ensure that the proper operation takes place as described, bywhich the directional relays always operate before the overcurrentrelays.

Fig. 5 shows the circuit arrangements of Fig. 4 in more detail so thatthey can be readily understood. In this figure the circuit-breakers CB1are provided with auxiliary contacts 1, 2, 3, 4 and 5, in addition tothe main contacts 6, '7 and 8; while the circuit-breakers CB2 aresimilarly provided with auxiliary contacts 9, 10, 11, 12, 13 in additionto the main contacts 14, 15, 16; the auxiliary contacts 1 and 2 and 9and are arranged to be closed before the main contacts 1 as theseconnect up the protective arrangements as will be understood from thefurther description. The three-phase power lines are represented by thereference L1, L2, L3. Three current transformers 0T1, GT2, GT3 areprovided one for for the purpose of supplying current to the overloadrelays 0L1, 0L2, 01.8 and to one winding of each pair of the three pairsof windings of the directional relay DB1. A voltage transformer VTl hasits primary leads connected respectively to each of the leads L1, L2, L3through suitable resistances and its secondary windings connectedthrough the auxiliary contacts 3, 4, 5 of the circuit-breakers CB1 tothe other windings of the directional relay DB1, these other windingsbeing connected, as is well known, across the phases each one 'is anexcess over a predetermined amount, the overload relay corresponding tothe line on which the excessive current occurs will be energized withthe result that one of the contacts 17, 18, 19 will be operated to openthe series circuit through these contacts and to close its asso--'ciated lower contacts which are connected in multiple with the lowercontacts of the other overload relays. It will be noted that with thisarrangement it does not matter whether one,

- two or all of the three relays 0L1, 0L2, 0L3 are operated exactly thesame circuit operation takes place, namely, the open ng of the circuitthrough the upper contacts and the closing of a circuit through thelower contacts. The circuit arrangemerits controlled by the relays 0L1,0L2, 01.3 and by the relay DRl are substantially identical with thosedescribed in connection with Fig. 4. The differential relay Di, theresistance 20, contact 21 and contact I all correspond to similar partsin left-hand side of the said figure. The right-hand side of the drawingis identical with the side, as will be noted, and includes currenttransformers 0T4, GT5, GT6 correspondto the current transformers CTl,GT2, GT3, the voltage transformer VTZ corresponding to the voltagetransformer VTl, the overload relays 0L4, 0L5, 0L6 corresponding to theoverload 0L1, 0L2, GL3 and the directional relay DB2 corresponding tothe directional relay DRl. The contacts 22, 23, 24 are arrangedsimilarly to the contacts l7, 18, 19. The directional relay DB2,resistance 25, contact 26 and contact 9 correspond to similar parts inFig. 4. The tripping coils of the circuit breakers are represented bythe references TCl and T62. The circuits of these coils in addition toincluding the contacts 21 and 26 respectively, also includes contacts 27and 28 respectively of the directional relays DRl and DB2 and thecontacts 2 and 10 respectively of the circuit-breakers. Beyond showingthree contacts 17, 18, 19 in place of one contact in the said Figure 4and showing the additional contacts 2 and 10 on the circuit-breakers thecontrolling arrangements associated with the pilot wire are similar tothose described in connection with Fig. 4 and it is thought unnecessaryto repeat the description in full in connection with this drawmg.

In Fig. 6 of the accompanying drawings, an arrangement is shown forprotecting the underground cable 1 running between stations A and B fromtwo different kinds of faults over a single pilot Wire PWl. For thispurpose use is made of quadruplex circuit arrangements using thevariations in strength of the effective current acting on thedifferential relays DA and DB for protection for faults of the kind inwhich voltage of the system is reduced to a very low value and using thevariations in direction of the resultant ampere turns influencing thepolarized differential relays PDA and PDN for protection from incipientfaults which do not ma terially affect the voltage of the system. Eachdifferential relay DA and DB is marginal and will operate only when theresultant magnetizu ing effect due to the combined effect of the twohalves of the windings exceeds a predetermined value. If the resultantmagnetizing falls a certain amount below the predetermined value therelay automatically restores.

Each polarized differential relay PDA and PDB is responsive to thedirection of the resultant ampere turns produced by currents flowing inits two windings. Thus if the currents flowing through the windings ofrelay PDA are such that the resultant magnetizing flux is downwards, therelay is restrained, while if the resultant magnetizing flux is upwardsthe relay operates. The same operating conditions apply to relay PDB.

The variations of strength of the effective currents are controlled inpart by directional relays DRA and DRB arranged to remain in thepositions shown when current is flowing into this section and severallyto take up the alternate positions when current above a predeterminedvalue is flowing out of the section at the respective ends thereof. Inconjunction with the directional relays overload relays OLA and OLB arearranged to operate when current above a predetermined value greaterthan the previously mentioned value flows into or out of the section.

It will be noticed that the batteries 7A and 7B alone are effective solong as either the respective directional relays or the respectiveoverload relays are in their upper positions, that is to say so long aspower is flowing out of the respective ends of the line section or solong as the flow of power past the respective overload relays is ofinsufiicient value to operate the same; only when the respectivedirectional relays and the respective overload relays are in their lowerpositions, that is to say, only when power is flowing into therespective ends of the line section and when the flow of power past therespective overload relays is of sufficient value to operate the sameare the associated batteries 6A and 63 made effective.

T1 and T3 are tripping coils for the circuit breaker CBA at station Aend of the line 10, whilst T2 and T4 are tripping coils for the circuitbreaker CBB at station B end of the line 10. The tripping coils T1 andT2 are respectively controlled by directional relay DRA and differentialrelay DA, by directional relay DB3 and differential relay DB and areeffective only when energized by the associated batteries 6A and 7A inseries and 6B and 7B in series respectively. Contacts 30A in the circuitof the tripping coil T3 are controlled by the polarized differentialrelay PDA whilst the direction of current flow through the coil iscontrolled by the reversing relay ERA and the tripping means associatedwith the coil is polarized so that it is effective only if current flowsthrough the coil from left to right although current from the associatedbatteries 7A only is sufficient to effect operation. Similarly contact23B of the circuit of the tripping coil T4 are controlled by thepolarized differential relay PDB whilst the direction of current flowthrough the coil is controlled by the reversing relay RRB and thetripping means associated with the coil is polarized so that it iseffective only when current flows through the coil from right to left,although current in the associated battery '73 only is sufficient toeffect operation.

W1 and KW2 are central zero kilowatt indicators (i. e. induction typewattmeters) measuring the power at each end of a section controlled bythe pilot wire PW. The pointers or equivalent members P1 and P2 areadapted to engage contacts 11A and 12B when the power measured by therespective indicators is flowing from station A to station B and isincreasing and to engage contacts 13A and 14B when the power flowing inthe same direction and measured by the respective indicators isdecreasing. On the other hand, if power is flowing from the station B tostation A and the power measured by the indicators is increasing, thepointers P2 and P1 respectively engage contacts 143 and 13A, but if thepower measured by the indicator is decreasing the pointers P2 and P1respectively engage contacts 12B and 11A. The contacts 11A and 13A andthe contacts 12B and 14B are mounted on a movable carriage controlled bymotors having fleld windings M1, M2, M3 and M4 in such a way that when apointer moves to engage a contact due to a change in the power flowingin or out of the section, the motors operate to move the contacts to anew position with the pointer out of engagement with both contacts. RAand RB are compensating resistances whilst RRA and RRB are reversingrelays biased to the positions shown but adapted to be moved to thereverse positions by energize.- tion of their respective windings.

Now normally the power measured at one end of the cable will be the sameas the power measured in the other end of the cable unless there is afault on the line. If a fault occurs the power flowing into the cable atone end will increase, while the power flowing out of the cable at theother end will decrease, that is to say, assuming that the leak takesplace when the power is flowing into the section at the left hand end,the indicator KWl will show an increase of power and contact 11A will beclosed. At the same time power, flowing out at the right hand end of thesection will be decreased and the contact 14B will be closed. A circuitwill therefore be completed as follows: battery, motor armature MAI,pointer P1, contact 11A, winding of reversing relay RRA, field windingM2, battery. The motor operates in this circuit so as to move contact11A away from the pointer P1, while the reversing relay RRA operates toreverse the polarity of the effective battery or batteries. Similarlyoperation occurs at the right hand end of the line, the reversing relayRRB being operated.

The following circuit conditions will now be considered. It has beenassumed that power is flowing into the section from the left hand endand flowing out from the right hand end. Consequently, in the absence ofany fault on the line section, relay DRA will be in the position shownwh le relay OLA will be, say, in the reverse position to that shown. Therelays OLB and DRB will, therefore, be in the reverse position to thatshown. Hence assuming that the value of power flow is constant underthese conditions, the following circuit will be closed over the pilotwire. Earth, contacts 15A, 17A, 18A, positive pole of battery 6A,battery 6A, battery 7A and then from negative pole of battery 7A throughcontact 19A to the mid point of differential relay DA. Here the circuitdivides, part of the current flowing through the lower winding of relayDA and the lower winding of polarized differential relay PDA andresistance RA to earth, while the other part of the current flows overthe upper windings of relays DA and PDA over the pilot wire PW, upperwindings of the relays PDB and DB to the mid point of the winding ofrelay DB, contact 22B, negative pole of battery '73, battery 7B,contacts 21B and 208 to earth. The direction of current .fiow over thepilot wire will be assumed from positive to negative and thus in thiscase would be from station B to station A. A circuit may also be tracedas follows: earth, contacts 20B and 21B, positive pole of battery 7B,battery '73, contact 22B, mid point of the winding of relay DB, lowerwinding of relays DB and PDB, compensating resistance RB to earth.

The resultant effect as regards relays DA, PDA, DB and PDB will now beconsidered.

With regard to relay DA, current will flow up- 1 wards through the lowerwinding and will depend for its strength on the voltage of the batteries6A and 7A in series. Current flows downwards in the upper winding ofrelay DA and its strength will I depend on the voltage of batteries 6Aand 7A in series with 7B which is connected up in opposition.Resistances RA and RB are compensating resistances which balance theresistance of the pilot wire and the upper windings of the relays at 1the other end of the pilot wire so that the currents will always be inproportion to the voltages in the respective circuits. Hence the currentthrough the upper winding of relay DA will be proportional to thevoltage of battery 6A while that through no the lower winding of relayDA will be proportional to the voltage of 6A and 7A. Hence the resultantmagnetic flux will be proportional to the voltage of 7A and relay DAwill remain unoperated since the magnetic flux will be insufficient tooperate 5 tion of the resultant magnetic flux is downwards the relaywill not operate, and hence will remain in the position shown.

With regard to relay PDA the magnetic flux in the two windings is in thesame direction but the resultant flux is downwards and therefore in thewrong direction as regards the operation of the relay and it will alsoremain in the position shown.

With regard to relay DB current flow is in an upward direction in bothwindings, the current flow in the lower winding proportional to thevoltage of battery '73, while that in the upper winding is proportionalto the voltage of battery 6A. The resultant magnetic flux will in thiscase be suflicient to operate relay DB. As relay DRB is operated,however, the operation of relay DB is of no effect at this time.

Consider now the case where there is no fault on the line and power flowincreases at both ends. Relay BRA will in this case be operated as wellas relays OLA, DRB and OLB. In this case the circuit over the pilot wirePW extends as follows: earth, contact 24A, negative pole of battery 7A,batteries 7A and 6A in series, contacts 18A, 17A, 25A, midpoint of thewinding of differential relay DA where the circuit divides, one branchpassing through the lower winding of the relays DA and PDA andresistance BA to earth. The other branch extends over the upper windingsof relays DA and PDA, the pilot wire PW, upper winding of relays PDB andDB, the mid point of the winding of relay DB, contact 223, negative poleof battery 7B and thence from the positive pole of battery 73 throughcontacts 21B, 20B to earth.

It will be noted that the efiect of this is to connect the batteries 7Aand 6A of the section battery 7B in series and in the same sense. Underthis condition a localcircuit at the station E end of the line may betraced as follows: earth,

. contact 20B, 21B, positive pole of battery 7B,

battery 7B, contact 22B to the mid point of differential relay DB andthen over the lower windings of relays DB and PDB and resistance RB toearth. The current through the upper winding is A sufficiently greaterthan the current through the lower winding to cause relay PDB toenergize and close contact 23B. A circuit can thereupon be traced asfollows: earth, contact 23B, tripping coils T4, contact 22B, negativepole of battery '73, battery 7B, contacts 21B and 203 to earth. Thetripping relay, however, is polarized and cannot operate when currentflows through thecoil T4 in this direction. Relay DB is also operatedbut since relay DRB is also operated this is of no eifect as regards theenergization of the trip coil T2.

With regard to relays DA and PDA, however, neither of these relays willoperate since the current flowing through the lower windings isproportional to the voltage of batteries 6A and 7A in series and is inopposition to the current flowing in the upper winding of the relays.Further, the current flowing through the upper windings is proportionalto the voltage of batteries 6A, 7A and 7B in series, and hence theresultant magnetic flux will be insuiiicient to cause the operation ofthese relays.

It will be clear that if the current flowing through the section were todecrease reversing relay BB2 would operate in the following circuit:

battery, motor armature MA2, contact 14B, reversing relay RRB, fieldwinding M3, to battery. The operation of reversing relay RRBunder'circuit conditions similar to those described above 1' wouldproduce some similar conditions to those described in connection withthe operation of relay BRA, but the relay DB will again operate to noeffect since relay DRB is still operated. Further, relay PDA willoperate instead of relay PDB but this'will also be without effectowingto the resultant direction of current flow in the trip coil T3.

If an earth fault occurs on the section, then currents through theindicator KW]. will cause it to indicate an increased current so as toenergizerelay RRA while the indicator KW2 will record a decreasedcurrent thereby energizing relay RRB. When both relays RRA and RRB areenergized and relays OLA, OLB and DRB are operated, the followingcircuit may be traced: earth, contact 24A, negative pole of battery 7A,batteries 7A and 6A in series, contacts 18A, 17A, 25A to the mid pointof the winding of differential relay DA. Here the circuit divides, onehalf passing through the lower winding of relays DA and PDA to earthover resistance RA, while the other half passes through the upperwinding of the relays DA and PDA, pilot wire PW" upper winding of relaysPDB and DB to the mid point of the winding of relay DB, contacts 26B,213,

positive pole of battery 73, battery 73, contact 24B to earth. A-circuitmay also be traced from earth contact 243, negative pole of battery '73,battery 7B, contacts 21B and 26B, mid point of winding of difierentialrelay DB and lower windings of relays DBand PDB to earth. With regard torelay DA, the current flowing through the windings is in opposition andhence the relay will not operate. The same applies to relay PDA, but theresultantmagnetic flux is upwards and proportional to the voltage of thebattery 6A so that this relay will operate. The current flow in the twowindings of relay PDB is in the same direction and since the resultantmagnetic flux is upwards this relay will also operate. Relay DB willalso operate since the current flow in the two windings is in the samedirection but the operation 01' this relay has no eifect since station Arelay PDA also operates because of the current flowing in the circuitdescribed through this lower winding and closes contact 30A therebycompleting a further tripping circuit as follows: earth, contact 30A,tripping coil T3, contacts 25A, 17A and 18A,positive pole of battery 6A,battery 6A, battery 7A, contact 24A to earth.

The current in this circuit is such as to operate the trip coil and thecircuit breaker CBA is tripped. It may be mentioned that relay DB isalso operated but is inefiective since relay DRB is operated.

If the fault occurs in the line section whilst the power flow issuflicient to operate the overload relays OLA, OLB, the reversing relaysERA and BBB and the polarized difierential relays PDA and PDB will,nevertheless be operated and, in view of the above description, theiroperation will be readily understood. Thus, whenever the power flowinginto the section AB from station A increases and at the same time thepower flowing out of the section from station B decreases, the sectionis isolated. As mentioned above, the tripping coils T1 and T2 arearranged so that they do not operate with current from battery 7A or '78only, but they operate when the associated directional relay is in theposition shown so as to connect battery 6A or 6B in series with battery7A or 7B respectively. Thus in the case when, for instance, relays DB,OLB and DRIB are operated, current from the battery 'TB will flowthrough the tripping coil T2 while the section is sound, as will bereadily understood.

It the flow of power through the line is from station 13 to station Aand an earth fault occurs so that the power flow at station B end of theline increases, while the power flow at station A end of the linedecreases then the pointer P1 engages contact 11A and the pointer P2engages the contact 143 whereupon reversing relays ERA and RRB areoperated and the faulty section is isolated by the tripping of thecircuit breakers at its opposite ends.

It, whilst no current is flowing in the line section a fault occurs sothat the power flow at both ends increases and the current flowinwardly, then pointer P1 engages contact 11A and pointer P2 engagescontact 14B. Reversing relays ERA and RRB, are therefore, operated andthe faulty section is isolated by the tripping of the circuit breakersat its opposite ends.

If, for any reason the kilowatt indicators KWl and KW2 and theassociated relays fail to give the protection for which they areprovided and the fault becomes sufficiently severe to cause the reversalof current in the line at that end thereof at which current was leavingthe line, then relays DA and DB are operated and efiect the isolation ofthe line section.

This application is a division of our copending application, Serial No.365,527, filed May 23, 1929.

What we claim is:

1. In an electric power transmission system an electric cable havingpower conductors and a pilot wire embedded therein, a source ofelectrical energy for supplying power to the power con- ,ductors of saidcable, apparatus located at one end 01' the cable for controlling thedisconnection of said cable from the system at that end in the event ofa fault occurring therein including a directional relay responsive tocurrent flowing in the power conductors at that end, an electromagneticrelay, a circuit-breaker and a tripping coil for said circuit breaker, asecond apparatus located at the other end of said cable including adirectional relay responsive to the current flowing in the powerconductors at said other end of said cable, an electromagnetic relay, acircuit-breaker and a tripping coil for said circuit breaker, auxiliarysources of electrical energy independent of said first source one ateach end of said cable, a circuit extending between the two ends of saidcable and including said pilot wire and said auxiliary sources ofelectrical energy to enable the directional relay of one apparatus tocontrol the electro-magnetic relays of the other apparatus and meanscontrolled by the directional relay at one end in response to particularcurrent conditions in said power conductors for closing a point in thecircuit of the local tripping coils simultaneously with it exerting acon trol over said pilot wire tending to cause the electromagnetic relayat the distant end to close a circuit in the said tripping coil at saiddistant end and means controlled by the directional relay at the otherend in response to particular current conditions in the power conductorsat said other end for closing a point in the circuit of a local trippingcoil simultaneously with it exerting a control over said pilot wiretending to cause the electromagnetic relay at the distant end to close apoint in the circuit of the tripping coil at the distant end, thecircuit arrangements being such that in the event of a fault in thepower line both switching devices will operate to cause the circuit ofthe tripping coils at each end to be completed.

2. In an electric power transmission system an overhead transmissionline, a source of electrical energy for supplying power to said line, astrand ed earthing wire for said line, an insulated pilot wire formingone of the strands of said earthing wire, apparatus located at one endof the line for controlling the disconnection of said line from thesystem at that end in the event of a fault occurring therein including adirectional relay responsive to current flowing in the line at that end,an electromagnetic relay, a circuitbreaker and a tripping coil for saidcircuit breaker, a second apparatus located at the other end of saidline including a directional relay responsive to the current flowing inthe line at said other end, an electro-magnetic relay, a circuitbreakerand a tripping coil for said circuitbreaker, auxiliary sources ofelectrical energy independent of said first source one at each end ofsaid line, a circuit extending between said apparatus including saidpilot wire and auxiliary sources of electrical energy to enable thedirectional relay of one apparatus to control the electromagnetic relaysof the other apparatus and means controlled by the directional relay atone end in response to particular current conditions in said line forclosing a point in the circuit of the local tripping coil simultaneouslywith it exerting a control over said pilot wire tending to cause theelectromagnetic relay at the distant end to close a point in the circuitof the tripping coil at said distant end and means controlled by thedirectional relays at the other end in response to particular currentconditions in the line at said other end and for closing a point in thecircuit of the local tripping coil si1nulthe circuit arrangements beingsuch that in the event of a fault in the line both switching de viceswill operate to cause the circuit of the tripping coils at each end tobe completed.

3. In an electric power transmission system an electric cable havingpower conductors and a pilot wire embedded therein, a source ofelectrical energy for supplying power to the power conductors of saidcable, a circuit-breaker at one end of said cable, a directional relayresponsive to the direction of current flowing at the other end of saidcable, a source of direct current of electrical energy arranged to beconnected in circuit with said pilot wire, a tripping coil for saidcircuit-breaker, a balancing circuit for said pilot wire, a differentialrelay controlling the .ii-l

ing over the pilot wire and said first winding of said differentialrelay without aifecting the current flowing through the said otherwinding to cause the differential relay to operate and close contacts inthe circuit of said tripping coil, and thereby control the operation ofsaid circuitbreaker to disconnect the power conductors at that end fromthe system in the event of a fault.

4. In an electric power transmission system an overhead transmissionline, a source of electrical energy for supplying power to said line, astranded earthing wire for said line, an insulated pilot wire formingone of the strands of said earthing wire, a circuit-breaker at one endof said line, a directional relay responsive to current flowing at theother end of said line, a source of direct current of electrical energyarranged to be connected in circuit with said pilot wire, a trippingcoil for said circuit-breaker, a balancing circuit for said pilot wire,a differential relay controlling the circuit of said tripping coil andhaving the end of one winding connected to said pilot wire and the otherwinding connected at one end to said balancing circuit and at the otherend to the other end of said first winding so that when said firstsource of electrical energy is connected to the junction of saidwindings equal currents flow over both windings and the relay isinoperative and means controlled by said directional relay for changingthe current flowing over the pilot wire and said winding of saiddifferential relay without affecting the current flowing through thesaid other winding to cause the differential relay to operate and closecontacts in the circuit of said tripping coil and thereby control theoperation of said circuit breaker to disconnect the power conductor atthat end from the system in the event of a fault.

5. In an electric power transmission system an electric cable havingpower conductors and a pilot wire embedded therein, a source ofelectrical energy for supplying power to the power conductors of saidcable, a source of direct current electrical energy, a polarized relayconnected to one end of the pilot wire, means for connecting said sourceof current to said pilot wire so as to cause current to flow thereoverand through said polarized relay in such a direction as not to affectits operation, a circuit breaker located at the same end of the cable asthe polarized relay, 2. tripping coil for said circuit-breaker, aswitching device located at the other end of said cable and responsiveto the direction of power flowing in the power conductors at that endand means controlled by said switching device for reversing thedirection of current flowing over said pilot wire to operate saidpolarized relay and in the event of a fault complete the circuit of thetripping coil so as to cause the circuit-breaker to open the cable atthe end where the polarized relay is located.

6. In an electric power transmission system an overhead transmissionline, a source of electrical energy for supplying power to said line, astranded earthing wire for said line, an insulated pilot wire formingone of the strands of said earthing wire, a source of direct currentelectrical energy, a polarized relay connected to one end of the pilotwire, means for connecting said source of current to said pilot wire soas to cause current to flow thereover and through said polarized relayin such a direction as not to affect its operation, a circuit-breakerlocated at the same end of the line as the polarized relay, 2. trippingcoil for said circuit-breaker, switching devices responsive to the powerflowing in said line at the other end to that at which the polarizedrelay is located and means controlled by said switching devices forreversing the direction of current flowing over said pilot wire toenergize said polarized relay and in the event of a fault effect theoperation of said tripping coil so as to cause the circuit-breaker toopen the line at the end where the polarized relay is located.

7. In an electric power transmission system an electric cable havingpower conductors and a pilot wire embedded therein, a source ofelectrical energy for supplying power to the power conductors of saidcable, a balancing circuit for said pilot wire, a differential relayhaving the end of one winding connected to said pilot wire and the otherwinding connected between said balancing circuit and other end of saidfirst winding so that when a source of electrical energy is connected tothe junction of said windings equal currents flow over both windings andthe relay is inoperative, a polarized differential relay having its 1windings connected in circuit with the windings of said differentialrelay respectively arranged so that when a source of electrical energyis connected to the junction of said windings equal currents flow overboth windings and the relay is I...

inoperative, means controlled by current flowing in said power line forvarying the strength of current flowing over the pilot wire and saidfirst windings of said polarized differential relay without affectingthe current flowing over said other 1 1 windings to cause saiddifferential relay to operate, means controlled by current flowing insaid power line for changing the direction of current flowing over thepilot wire and said first windings of said differential relay and saidpolarized 3 differential relay without affecting the current over saidother windings to cause said polarized differential relay to operate andmeans controlled by said differential relay to cause the power line tobe opened at the end where the differential rewith respect to the powerconductors that in the 1' case of an accident to the power conductorsthe pilot wire may be broken, a source of electrical energy forsupplying power to the power conductors of said line, directional relayslocated at each end of said line controlled in accordance with thedirection of power flowing in the lines at the ends thereof, deviceslocated at each end of said line variably responsive according to theamount of power flowing in said power conductors at the ends thereof,balancing circuits for the pilot wire located at each end of said line,differential relays and polarized differential relays one of each beinglocated at each end of said line each relay having a winding connectedin series with the winding of the other relay and with the balancingcircuit at that end and the other windings connected in series with thepilot wire, sources of direct current electrical energy at each end ofsaid line arranged to permit of different potentials being applied tothe pilot wire at each end, means at each end i controlled by thedirectional relays at the same ends for connecting either low potentialor high potential from the sources of electrical energy to the junctionpoints of the two sets of windings of the polarized and differentialrelays at each and causing the circuit-breakers to isolate the sectionwhen the direction of current flowing in the power lines is in oppositedirections or varies in amount at the two ends indicative of a fault onthe line.

REGINALD OTTO KAPP.

CHARLES GEORGE CARROTHERS.

